Lithium-ion secondary batteries high in energy density have traditionally been developed for use as motive power sources for electric automobiles, for example. Notably, prismatic secondary batteries having high volumetric densities are known as secondary batteries that are mounted on vehicles and the like. These prismatic secondary batteries are formed as follows: a positive electrode pre-coated with a positive electrode active material on both sides of a positive electrode foil, and a negative electrode pre-coated with a negative electrode active material on both sides of a negative electrode foil are flatly wound together with a separator intervening the positive and negative electrodes. And then, this wound body (electrode group) is stored in a prismatic battery casing.
In such a prismatic secondary battery, after a positive electrode metallic foil and a negative electrode metallic foil at both ends of the wound body are exposed in a direction of its winding axis, metallic foil exposed sections are formed. Then connecting electrode terminals and current-collector bodies to the metallic foil exposed sections by welding or the like minimizes lengths of current-flow pathways to thereby cause lower connection resistance.
In a case where a horn and an anvil are used to hold a metallic foil exposed section and current-collector body and weld them, pressing force upon the horn would deform the anvil and cause a welding defect to occur between the metallic foil exposed section and the current-collector body when, for example, the anvil is cantilever-supported.
To solve such a problem, Patent Document 1 discloses a technique for welding a metallic foil exposed section and a current-collector body together after dividing the metallic foils of the metallic foil exposed section of a wound body into two sections to reduce the number of metallic foils sandwiched by the horn and the anvil.